Ground-water and rainfall data for the period October 1987 through September 1997 from Tutuila and Aunuu, American Samoa, are plotted in time-series graphs and summarized. The data include pumpage and chloride concentrations from 53 production wells on Tutuila, including 5 new wells that were put into production between October 1996 and September 1997, 3 production wells on Aunuu, water-level measurements from 16 wells on Tutuila, and rainfall data from 2 gages on Tutuila.
Mean annual rainfall was 164 inches at the gage in Afono and 210 inches at the gage in Aasufou during the period October 1987 through September 1997. Rainfall in the 12-month period from October 1996 through September 1997 totaled 210 inches at the Afono gage and 234 inches at the Aasufou gage.
In the Tafuna-Leone Plain, most wells were pumped at rates from 0.2 to 0.5 million gallons per day and had chloride concentrations usually less than 500 milligrams per liter. In the 12-month period ending September 1997, the combined pumpage from wells in the Tafuna-Leone Plain was about 6.3 million gallons per day and the chloride concentrations in most wells remained below 200 milligrams per liter. In Aasufou, wells produced 0.04 to 0.05 million gallons per day and chloride concentrations remained near 15 milligrams per liter.
Most wells in central and eastern Tutuila were pumped at rates less than 0.1 million gallons per day. Wells in the Fagatogo, Pago Pago, and Aua areas, which averaged more than 0.4 million gallons per day of pumpage, are exceptions. Some wells in central and eastern Tutuila had chloride concentrations that frequently exceeded 500 milligrams per liter. In the 12-month period ending September 1997, chloride concentrations in the production wells in Aua rose to the highest levels on record. In the 12-month period ending September 1997, water levels in Tafunafou, Iliili, Pago Pago, and Laulii remained at about the same elevation above mean sea level as in previous years, water levels in Aua remained below mean sea level as in previous years, and water levels in Malaeimi and Fagaalu declined relative to previous years.
The three production wells on Aunuu have been pumped at various rates less than 0.1 million gallons per day and had chloride concentrations usually in excess of 500 and often in excess of 1,000 milligrams per liter.
Additional Publication Details
USGS Numbered Series
Summary of Ground-Water Data for Tutuila and Aunuu, American Samoa, for October 1987 Through September 1997